Three-dimensional (3D) printing is an additive printing process used to make three-dimensional solid objects from a digital model. 3D printing is often used in rapid product prototyping, mold generation, and mold master generation. 3D printing techniques are considered additive processes because they involve the combined application of successive layers of material. This is unlike traditional machining processes, which often rely upon the removal of material to create the final object. Materials used in 3D printing often require curing or fusing, which for some materials may be accomplished using heat-assisted extrusion or sintering, and for other materials may be accomplished using digital light projection technology.